Transurethral prostate resection requires the utmost care to avoid undesirable outcomes, which, in extreme cases, may even include death of the patient.
The main risk is that the circulatory system will absorb the clarificant if internal pressure exceeds a certain limit known as the absorption threshold.
This risk is characterized by acute hemodilution of the surgical patient.
Thus, the surgeon must know the internal bladder pressure and control it constantly in order to modify the flow and suction rate of the irrigation fluid.
Several techniques already exist in the art for controlling distribution and recovery of liquid clarificant evacuated from the cavity of the human body through an endoscope or a resectoscope. Noteworthy among these are U.S. Pat. No. 3,900,022 (WIDRAN) as well as French Patent No. 2.642.297 (SYNERGIE) and European Patent Publication No. 0224487 (BURNER).
The WIDRAN U.S. patent, issued in 1975, relates to the circulation of an isotonic liquid clarificant for a resectoscope throughout the surgical zone. The circuit passing through the resectoscope has an irrigation network consisting of a series beginning with a reservoir and thereafter, a pump, a pressure regulator, a valve, and a pressure indicator and limiter. The suction network comprises the same elements arranged in series, but in the opposite order, leading to a collection device.
Flow is regulated manually through an inlet valve and an outlet valve. The pressure limiter is simply designed to prevent excessive pressure and the pressure regulator is provided to eliminate periodic pressure spurts caused by the peristaltic pump.
This regulator is not assigned to any specific pressure or flow speed in either branch of the circuit. The pressure restriction is merely a safety limit, that is, a cut-off point. The pressure sensor-display is purely visual. It merely displays pressure values during the procedure.
It is apparent that in this invention there is no automatic pressure or flow regulation based upon actual internal pressure within the cavity.
Flow is regulated manually based upon only the pressure displayed, without taking into account the fact that additional blood and urine flow at random during the intervention.
In summary, to be safe, irrigation flow should be controlled only when internal pressure within the cavity is taken into account. Obviously, WIDRAN is unable to either determine or apply this variable governing flow control. WIDRAN's invention takes into account neither the decrease in weight within the circuit and the instrument, nor incoming blood and urine during the procedure, and therefore the displayed pressure fluctuates, varying considerably from the internal pressure.
Regulating flow manually on the basis of the displayed pressure is too inaccurate to be safe for the patient.
Thus, the disadvantages outlined above remain unresolved.
According to the invention described in French Patent No. 2.642.297 filed by the French company SYNERGIE, the resectoscope and therefore the cavity are irrigated with previously heated liquid, the temperature of which is regulated by a thermostatically controlled bath.
This invention is based on the fact that the hemostatic effect desired for coagulation depends upon temperature and that consequently an isotonic liquid which has been heated to a temperature of 42.degree.-45.degree. C. decreases hemorrhaging and thereby the flow rate of the clarificant.
In addition, this invention purports to decrease the risk of absorption of the liquid clarificant by the circulatory system merely by limiting pressure to the maximum regulable value.
Following are some specific characteristics of this invention.
The irrigation network consists of a thermostatically controlled water bath and thereafter, a simple peristaltic pump controlled with a manual keypad. A piezometric cell for measuring excessive pressure is next in the series, followed by a flow regulator and a depression pump. The flow regulator is a throttle-type regulator activated by a pneumatic device which is supplied by the depression pump. The excess pressure control means acts upon the throttle and the peristaltic pump using data from the piezometric cell to control suction and to cut off the irrigation pump if there is excess pressure, i.e., if the pressure exceeds a certain limit.
Two flow sensors, one at the inlet and one at the outlet of the resectoscope, are connected to a processor and a display trait which indicates instantaneous flow rates and differences between them, and also integrates and stores the data to yield a variable for detection of any absorption of the liquid clarificant by the circulatory system. This variable is taken into account in acting upon the pump and the suction flow.
The SYNERGIE invention utilizes the actual pressure value in the suction circuit as an indicator of whether the threshold has been exceeded for stopping the pump. The invention also utilizes the upstream and downstream flow rates in relation to the cavity and the difference between them to determine whether the safety threshold has been attained and to regulate the device.
The above method of regulation and detection by measuring pressure in the suction line and controlling flow fails to ensure perfect vertical pressure control for the following reasons:
there is no way to correct for decreased pressure in the suction line as a function of flow; PA1 it is not possible to measure pressure when the inlet of the resectoscope is blocked by contact with tissue in the urinary tract; PA1 pressure measurement becomes unreliable during frequent gaseous emissions which occur throughout resection when tissues are cut and cauterized. Moreover, because of their design, resectoscopes are often not watertight; PA1 absorption begins once a certain pressure limit is attained--this limit can vary depending upon the flow through the instrument, operating conditions and the patient's morphology; and PA1 flow control does not take into account the urine produced by the kidneys during the intervention. PA1 the exact interior bladder pressure is known at all times, having been calculated from the data regarding pressure loss within the irrigation and suction networks, and because various properties of the instrument have been stored in memory before the outset of surgery. The calculation device continuously furnishes exact internal pressure values on the basis of the stored data; PA1 the flow of irrigation fluid can be constantly regulated because the interior cavity pressure is known and the pressure can be brought to an optimal value using the appropriate automatic command on the irrigation and suction pumps. The work zone corresponds to the self-regulating pressure system in which the pressure is regulated by acting upon the suction pump; PA1 pressure spurts caused by withdrawing the endoscope from the operating zone and obstruction of the suction orifice during contact with the adjacent wall or, more rarely, because tissue fragments are introduced, automatically cause higher pressure, whereby the suction rate increases during a first phase and then increases again during a second phase, until a maximum suction flow rate and a pressure limit called the safety limit are attained.
Thus, by failing to correct for pressure loss, a supplementary pressure error is introduced and of the suction inlet is blocked or obstructed as it often is during the surgical procedure, the pressure sensor on the suction circuit is depressed, becoming unreliable or even useless. The system reacts in a disorganized manner to unknown or blocked data and is unable to exert the required control for a certain time period.
Thus the SYNERGIE system cannot continuously monitor the internal, actual pressure within the cavity, which is the only useful basis for regulation,
BURNER describes elaborate means for automatically regulating the pumps on the irrigation and suction circuits using pressure within the irrigation and suction circuits and taking into account various pressure corrections such as static pressure and a correction corresponding to pressure loss within the instrument.
Additionally, for safety reasons, when the pressure exceeds a maximum acceptable level controlled by the surgeon, the comparator connected to the control unit stops the irrigation pump and thus the flow of fluid into the instrument or slows the apparatus to minimal functioning level.
The apparatus is completed by a volummetric counter with an audible signal which alerts the surgeon to the flow rate and stops the irrigation fluid when the total predetermined amount required for the process has been used.
The suction branch consists of a circuit similar to the irrigation branch with pressure correction to control the pump on the basis of pressure loss within the instrument, while also taking into account static pressure and providing the same function which limits pressure to the maximum tolerated.
This device provides for pump control based upon a corrected pressure value assumed to be that which prevails inside the cavity, as it relies on the pressure existing at the upstream inlet of the endoscope corrected for pressure loss within the instrument. However, this value is not a reliable or exact indicator of internal pressure due to pulsations and pressure fluctuations coming from the peristaltic pumps required for the apparatus to work with liquids used either to inject the patient internally or for external circulation.
Furthermore, when function is dependent upon such volume values, no allowance is made for body fluids flowing into the cavity, such as blood or mine produced by the kidneys during bladder surgery.
Thus, considerable uncertainty persists and it is possible for absorption into the circulatory system to occur without anyone being aware of it.
BURNER also fails to take into account gaseous emissions which falsify flow rate measurements. The use of an electronic bistoury causes such gaseous emissions dining resection and cauterization.
Finally, BURNER bases his entire theory of real time regulation on an irrigation pump delivering a continuous flow. In his method correction is based upon only one variable signal, which is assumed to be non-undulating. However, to prevent infection and for other reasons of hygiene and prophylaxis, the use of peristaltic pumps is obligatory in the medical field.
Under such conditions, the apparatus of the BURNER patent is not sufficient to provide the permanent, specific information regarding actual interior cavity pressure which is necessary for precise, reliable flow regulation and to ensure the patient's safety.